Top Astronomy Stories of 2003

By Kathy Svitil, Jeffrey Winters|Friday, January 02, 2004
oldplanet11
oldplanet11

Formed a billion years after the Big Bang, the universe’s oldest and most distant known planet circles a collapsed star, or pulsar (green circle), in the globular cluster M4, which is 5,000 light-years away from Earth.

Courtesy of NASA/H. Richer/University of British Columbia

Good News for Space Aliens

In July an international team of scientists announced that they had found the oldest planet ever sighted, an important discovery because it suggests that the chances of finding life elsewhere in the universe are much more likely.

Planets had been thought of as latecomers to the cosmic party, created a long time after galaxies and stars and only when heavier elements, like carbon and silicon, had accumulated in the universe. But this 12.7-billion-year-old planet, an enormous gaseous sphere more than twice the mass of Jupiter, puts that view to rest.

Astrophysicists have known something was in that spot since 1992, when radio signals suggested a presence. But most assumed the unknown mass was simply a small star or a brown dwarf, especially since it is located in M4, a globular cluster thought not to have heavy elements. Researchers were shocked when astrophysicist Steinn Sigurdsson of Pennsylvania State University concluded that the object was a planet, based on a series of Hubble Space Telescope observations.

Sigurdsson and his colleagues have retraced the unnamed planet’s colorful history in detail. It had formed around a yellow star located at the outer fringes of M4. Then about 2 billion to 3 billion years ago, it and its star migrated toward the crowded center of the cluster and encountered a neutron star paired with a white dwarf.

The neutron star captured the planet and its sun, the white dwarf was bounced out, and the entire system was flung toward the outskirts of the cluster. The yellow star eventually evolved into a red giant and transferred its mass to the neutron star, which sped up to become a pulsar. The red giant turned into a white dwarf. Today we can see this white dwarf, along with the planet, orbiting the pulsar.

In another billion years, Sigurdsson predicts, the system will migrate back to the center of the cluster, where encounters with other stars will rip the group apart, “leaving the planet to float, by itself, in the spaces between the stars,” he says.

The presence of the relic suggests that very early planet formation was common, says Sigurdsson. This means that life could well have evolved around 5 billion or 6 billion years earlier than anyone had expected.

--Kathy Svitil

gammabef17
gammabef17
A satellite observatory alerts astronomers to one of the most enigmatic high-energy acts in astronomy: a gamma-ray burst. (A) The spot before the 30-second flash begins. (B) The burst leaves an optical afterglow.
Pete Challis/Harvard Smithsonian Center for Astrophysics

Gamma-Ray Burst Source Located

In April a team of astronomers finally confirmed the origin of mysterious high-energy bursts of gamma rays that randomly pervade the universe about twice a day. The discovery began at 6:37 a.m. on March 29, when Harvard astronomer Krzysztof Stanek’s pager beeped. It was NASA’s High Energy Transient Explorer satellite calling.

The probe had spotted a powerful flash of gamma rays in the constellation Leo. Within seconds Stanek and other researchers around the world obtained the coordinates so that they could train their telescopes on the burst—the brightest ever detected by the High Energy satellite.

At its peak, the burst was so powerful it was almost visible to the naked eye, emitting a 100 million trillion times more radiation than a solar flare. “In just a few seconds, it produced as much energy as our sun would produce in 10 billion years,” Stanek says.

Astronomers had theorized that gamma rays are born when a large supernova, called a hypernova, spits out jets of material that interact with a star’s outer layers. But no one had empirical proof because gamma-ray bursts are so fleeting and difficult to pinpoint.

This time, Stanek and his colleagues instructed the 6.5-meter Multiple Mirror Telescope, atop Mount Hopkins in Arizona, to collect a detailed spectrum over 12 days following the event. Astronomers calculated that if a supernova spawned a gamma-ray burst, a distinctive type of light would appear during the following week. “That is exactly what happened,” Stanek says. “And each day, as the supernova got stronger, the lines [in the spectrum] evolved. There is no doubt there is a supernova there and that it caused the burst. This clinches the case.”    

--Kathy Svitil 

 

Signs of Primordial Star Ignition Detected

Late in 2002, Wolfram Freudling and two colleagues grabbed some observing time on the Hubble Space Telescope to study the universe’s pristine early days, before exploding stars seeded interstellar space with heavy elements. The results, announced in April, confounded their expectations. Less than a billion years after the Big Bang, the cosmos already showed notable signs of stellar contamination, meaning that the first stars lit up much sooner than astronomers believed.

Hubble’s infrared camera enabled Freudling, an astronomer with the European Southern Observatory in Garching, Germany, to analyze the elements in three quasars—clouds of hot gas swirling into giant black holes—that were up to 12.8 billion years old.

According to standard models, the first stars needed at least 500 million years to begin lighting up and another 700 million to 1 billion years to manufacture heavy elements such as iron and spread them through space. Freudling therefore expected that gas around the quasars, which were shining when the universe was just 900 million years old, would be metal-free.

Instead, he and his colleagues found the quasars are surrounded by copious amounts of iron. That means the first stars must have lit up just 200 million years after the Big Bang, a number that dovetails nicely with new results from the WMAP satellite. Together, the two sets of data show that the universe is unexpectedly efficient at building stars. “The next step will be to find and measure quasars farther in the past,” Freudling says. Eventually he hopes to discover when the first stars ignited.

--Kathy Svitil 

2mass56
2mass56
2MASS Project/T.H. Jarrett, R. Hurt, J. Carpenter, and J. Mazzarella

Presto! Space-Time Blurriness Vanishes

Physicists have been knocking themselves silly devising theories to show how, in the tiny world of electrons, quarks, and gluons, the fabric of space is full of gaps and time appears jittery. Perhaps they can relax now. In February a team of astrophysicists showed that time and space may be smooth after all.

Using the Hubble Space Telescope, Richard Lieu of the University of Alabama at Huntsville and his colleagues snapped images of a galaxy located 4 billion light-years away. It was a perfect test case: The “foamy” texture of space-time was expected to slightly alter the speed of light waves as they traveled across such a vast distance.

Collectively, the effect would be to throw the waves of light from the galaxy out of phase; waves that started out even and lined up would be out of step with one another when they reached Earth. Lieu expected this effect would produce a slight blurry distortion around the galaxy. Instead, he saw a distinctive pattern that can be produced only if all the light reaches the telescope at precisely the same time. No blurriness, no foaminess.

The results, which were reproduced in March by a separate European team, raise serious questions for astronomers as well as physicists. If space-time is smooth, black holes cannot exist, and the Big Bang couldn’t have happened. “Without fuzziness, all of the matter and energy of the universe has to be packed, at the moment of creation, into a volume that is zero, with infinite temperature and infinite density. It is an impossible thing to contemplate, and it cannot be reconciled with the current Big Bang theory,” Lieu says.

The theorists are not worried. “The best models of quantum gravity are not ruled out by these results,” says Lee Smolin of the Perimeter Institute, a nonprofit physics institute in Waterloo, Ontario. Y. Jack Ng, a theoretical physicist at the University of North Carolina at Chapel Hill, regards the findings as fundamentally flawed.

Space-time foaminess will have a random effect on light waves, he says, speeding them up at some times and slowing them down at others. Because of this mixed effect, a wave will fall out of phase with its neighbors much more slowly than Lieu’s team figured. “They overestimated the cumulative blurring effect, by a factor of at least a thousand trillion,” Ng says. “No wonder they didn’t find it.”

--Kathy Svitil

 

We Can See Clearly Now

The Milky Way galaxy is so dusty that most light telescopes can’t get a sharp picture of it. However, the Two Micron All Sky Survey (2MASS), begun five years ago, has been exploiting the ability of longer-wavelength infrared light to slip past the debris and create clearer images.

In March a dramatic composite portrait based on millions of images collected by two 1.3-meter telescopes in Arizona and Chile was released. At the center is the Milky Way galaxy; the rusty blush through the middle is composed of dense dust clouds. More than 1 million galaxies, color coded by distance, also appear.

Those in blue are nearest, the green are at a moderate distance, and the red are farthest away. The portrait shows “the texture of the universe,” says Michael Skrutskie, head of the survey’s science team. “It is a relic of the beginning of the universe, when tiny fluctuations in density grew to become clusters of galaxies, and filaments of clusters, and voids between filaments. By analyzing the distribution of galaxies in the sky, we can tell something about what those original fluctuations were.”         

--Kathy Svitil

 

Neptune Rocks Early Solar System

Today our solar system looks calm and orderly, but Rodney Gomes has found evidence of its chaotic beginnings. Gomes, a planetary scientist at the National Observatory in Rio de Janeiro, has been studying the Kuiper belt, a group of asteroids orbiting beyond Pluto. In February he announced that some of these objects originated much closer to the sun but were exiled into darkness by Neptune’s gravity.

Astronomers have recently realized that the Kuiper belt contains two populations. One consists of grayish rocks that circle the sun in the same plane as Earth. The other, a rakishly red group, zings around on trajectories tipped as much as 40 degrees from horizontal. The origin of the off-kilter bodies has been a mystery. To have their orbits so skewed, these asteroids must have encountered something with serious gravitational oomph—a planet, for example. Neptune has the requisite mass, but it seemed too far away to cause trouble.

When Gomes ran computer simulations, he realized Neptune probably was the culprit after all. The second group could have formed near Neptune and then been knocked out to distant, tipped orbits when they inched too close to the planet. Gomes’s model implies that the other Kuiper belt objects might also have formed far closer in than they are now. “This means that the disk from which the planets formed was much more compact than usually supposed, with an outer edge where Neptune is today,” Gomes says. “These findings may have implications for how planetary systems around other stars could form and where and how big the planets would be.” 

--Kathy Svitil       

 

Neutron Star Fizzles

The fate of most stars in the universe, including our own sun, is to implode, collapsing from a huge mass millions of miles across into a sphere barely 10 miles wide that spins around hundreds of times a second. Most of what astrophysicists know about these curious remnants, called neutron stars, is based on theory and limited observations. So researchers were startled to learn in June that the first good measure of a young neutron star’s magnetic field defied all predictions.

Giovanni Bignami, director of the Centre d’Etude Spatiale des Rayonnements in Toulouse, France, aimed a sensitive camera aboard the XMM-Newton orbiting X-ray observatory at a young neutron star labeled 1E1207.4-5209. After three days of tracking, Bignami and his colleagues had collected a detailed X-ray spectrum and a good look at the star’s magnetic field.

Theory predicts that what neutron stars lack in size, they more than make up for in strong magnetic fields, which result from charged particles crackling through the iron crust surrounding the hideously dense ball of uncharged neutrons within the star. Although a typical star has a magnetic field of about 100 gauss, neutron stars are thought to have magnetic fields of up to 1 trillion gauss. But Bignami’s team calculated that the magnetic field of 1E1207.4-5209 is one-thirtieth as strong as it should be. “Either it means that the theory is wrong,” says Bignami, or the star “might have a debris disk around it, like a protoplanetary disk or an overgrown system of Saturnian rings, which could create the same effect.”

--Kathy Svitil

 

Plasma Devils Brighten the Sun

In June a team of astronomers announced that new images of the sun’s surface could explain why our star brightens and dims over the course of an 11-year cycle. Using a Swedish telescope built to study the sun exclusively, the researchers recorded enormous walls of plasma, or roiling superheated gases. They extend 200 miles high and up to 1,000 miles wide, covering the sun’s surface like a sheet of bubble wrap.

The team, led by Bruce Lites of the National Center for Atmospheric Research in Boulder, Colorado, and Tom Berger of Lockheed Martin Solar and Astrophysics Laboratory in Palo Alto, California, reported that the sides of the plasma walls were much brighter than their tops. When more of the walls form during the peak of the solar cycle, more of these bright sides can be seen along the rim of the sun. As a result, more of the sun’s radiation heads toward Earth.

“We need to understand exactly what the magnitude of this [radiation] is and whether it is having any effect on our climate,” Berger says.    

Jeffrey Winters

sun-82
sun-82
A telescopic image of the sun’s turbulent surface reveals a section of the rim that extends roughly 230 million square miles. The white pinpricks indicate the edges of superheated walls of gas.

Goran Scharmer and Mats G. Löfdahl/Institute for Solar Physics of the Royal Swedish Academy of Science

Plasma Devils Brighten the Sun

In June a team of astronomers announced that new images of the sun’s surface could explain why our star brightens and dims over the course of an 11-year cycle. Using a Swedish telescope built to study the sun exclusively, the researchers recorded enormous walls of plasma, or roiling superheated gases. They extend 200 miles high and up to 1,000 miles wide, covering the sun’s surface like a sheet of bubble wrap.

The team, led by Bruce Lites of the National Center for Atmospheric Research in Boulder, Colorado, and Tom Berger of Lockheed Martin Solar and Astrophysics Laboratory in Palo Alto, California, reported that the sides of the plasma walls were much brighter than their tops. When more of the walls form during the peak of the solar cycle, more of these bright sides can be seen along the rim of the sun. As a result, more of the sun’s radiation heads toward Earth.

“We need to understand exactly what the magnitude of this [radiation] is and whether it is having any effect on our climate,” Berger says.    

Jeffrey Winters

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